Backfire / popping on acceleration

Discussion in 'Troubleshooting & Diagnosis' started by Tphil413, Dec 2, 2017.

  1. Tphil413

    Tphil413 Veteran Member

    234
    0
    Jun 1, 2007
    San Francisco, CA
    OK this one has me stumped. Car has run great for a while now, then suddenly one morning its starts backfiring as I accelerate and decelerate. Not a loud timing backfire but more of a popping sound. I thought it might be my air:fuel mixture so I tuned it and no improvement. Checked the timing and all looks good. Read on a few threads that popping could be due to an exhaust leak igniting unburnt fuel. Seemed like a possibility as my headers drop down below my frame and are flat and scuffed us from hitting speed bumps. One may have finally given way. But I don't hear a ticking sound like a header gasket leak so I'm not sure.

    I also read about backfires from fuel ignited in the engine and was doing a visual check today and noticed that manifold gasket is bulging out about a 1/4" between the number 3 and 5 cylinders. Looks like its covered in oil. I also have been noticing the car running through oil quickly. Could a manifold gasket leak be causing fuel to ignite and cause a backfire? Could oil be getting into the 3 and 5 cylinders? My son drive the car and said he occasionally saw smoke from the rear of the car.

    Just need a place to start...any thoughts?
     
  2. ULTM8Z

    ULTM8Z Veteran Member

    8,272
    45
    May 19, 2000
    Los Angeles
    Check your plug wires. Ohm them out and see if one is way out of family in terms of impedance. I've had instances where a faulty plug wire causes what you're describing.

    Another possibility is a ruptured accelerator pump diaphragm or some other AP malfunction that's causing a lean tip in.
     
  3. SRGN

    SRGN Veteran Member

    262
    67
    Feb 20, 2009
    Central NJ
    Usually popping in the intake means lean mixture or a dead exhaust cam lobe, assuming everything's good with ignition.
     
    Plant Engineer likes this.
  4. Tphil413

    Tphil413 Veteran Member

    234
    0
    Jun 1, 2007
    San Francisco, CA
    Pulled the number 3 plug and it looks like something is happening there. Here's a pic of the plug and the manifold gaskets. Not sure what's going on here, maybe a ruptured manifold gasket is allowing oil into the cylinder?

    IMG_1541.JPG IMG_1542.JPG IMG_1550.JPG
     
  5. SRGN

    SRGN Veteran Member

    262
    67
    Feb 20, 2009
    Central NJ
    Pull the valve cover. With the ignition off, use a starter switch to crank the engine. See if the valves on #3 move the same amount as the rest.
     
  6. MotionClone

    MotionClone Veteran Member

    1,279
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    Jan 20, 2014
    away from the crazies
    listen for vacuum leak near those bulged intake gaskets
     
  7. Tphil413

    Tphil413 Veteran Member

    234
    0
    Jun 1, 2007
    San Francisco, CA
    And here's the #5 plug...

    IMG_1557.JPG IMG_1558.JPG
     
  8. Tphil413

    Tphil413 Veteran Member

    234
    0
    Jun 1, 2007
    San Francisco, CA
    Correction pics were of #4 and #6 plugs
     
  9. ULTM8Z

    ULTM8Z Veteran Member

    8,272
    45
    May 19, 2000
    Los Angeles
    Uh oh....You may have a blown head gasket at the #4 and #6 cylinder.
     
  10. Tphil413

    Tphil413 Veteran Member

    234
    0
    Jun 1, 2007
    San Francisco, CA
    Or could it just be a blown manifold gasket? These RPM Airgap manifolds are hard to torque accurately. No easy way to get a torque wrench on the two center bolts. I don't see any coolant in the oil. Car isn't running hot.
     

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